Ohio's Early Vote: Nate Silver Gulps

This is a little complicated, but the polls have been claiming around 35% of the Ohio population has voted early. Rasumssen even pegged it at 40%.

Conservatives have been saying for a while that the polls were skewed because too many people were saying they'd voted early. Either they were a self-selecting unrepresentative sample -- perhaps so jazzed about voting they were much more eager to talk to a pollster for a half an hour or 40 minutes -- or a lot of people were just claiming "I already voted," even though they didn't.

Assuming Ohio will produce a 2004 level of turnout, early voting in fact accounts for only 32% of all votes which will be cast. Assuming a 2008 level, early voting accounts for only 31% of all votes which will ultimately be cast.

And note that if voting exceeds 2008, somehow, that pushes the fraction of early voters down even further.

The next important piece of data is what the polls consistently report: Obama leads by huge margins among early voters but trails Romney among those who say they will vote on election day. This inverse in voting segments is why the proportion of early votes in the total votes — and that virtually every poll overestimated this proportion — is so tantamount. In most polls (which usually only have Obama leading by a small margin, although some give him a more comfortable ~+5%), lowering the percentage of early votes in the polling sample means lowering Obama’s lead drastically. And when Obama’s lead is only one or two percentage points, that can mean handing the election to Mitt Romney.

It also makes the polls suspect.

But Nate Silver shrugged it off:

In a discussion on Twitter, Silver and Wasserman focused largely on the surprise changes in turnout in many of Ohio’s counties. While total early voting in Ohio only increased by 2.44% from 2008, early voting in counties that voted heavily for Kerry/Obama declined 4.1% while counties that voted heavily Bush/McCain increased their early voting by a shocking 14.39%. Wisserman, while still predicting an Obama victory, suggested that trend meant a tighter race in Ohio than expected and suggested it might undercut Nate Silver’s famous forecast. Nate Silver’s response: “I’ll stick with the 538 forecast in OH. I disagree that the early voting data there provides much reason to doubt the polls.”

While some people are turning to counting the votes, Nate Silver is still just looking at the polls.